In danger of losing five straight starts for the first time in more than eight years, the right-hander tries to put an end to his woes in Wednesday's finale against the Milwaukee Brewers at Miller Park.
Westbrook (7-8, 4.35 ERA) is doing all he can to end a stretch in which he's 0-4 with a 10.13 ERA, having allowed 29 hits, walked 15 and struck out 10 in 21 1-3 innings.
"It's always frustrating when you don't give your team a chance to win and do your job, which I haven't been able to do the last couple outings," said Westbrook, who dropped his first five starts in 2005.
He gave up seven runs and walked five Friday in 6 2-3 innings of a 7-0 road loss to the Chicago Cubs, but that was not enough for Matheny to pull him from the rotation.
"I know it's frustrating to him and baffling to us on how to put that all together," Matheny told the Cardinals' official website. "He said, physically, he feels good.
"It's just quality pitches right from the get-go. The guy is such a pro, and he's going through a thousand different things in his mind of what he can do differently."
Westbrook was solid at Milwaukee on May 2 when he allowed a run, six hits and walked three in six innings of a 6-5 victory.
He hopes to help wild-card-leading St. Louis (72-53) get back on track after its three-game winning streak ended with a 6-3 loss at Milwaukee on Tuesday. Rookie Kolten Wong had three hits and Yadier Molina hit a two-run homer, but the Brewers (55-71) scored five times in the fourth to erase a 3-0 deficit.
"I know we have a stretch here where we're playing a lot of teams that are contending for playoff spots,'' winning pitcher and ex-Cardinal Kyle Lohse said. "Feels good to kind of hurt teams' chances.''
After going 0 for 5 on Thursday in his return from missing two weeks with a sprained knee, Molina is 10 for 18 with five doubles and two homers to raise his average to an NL-leading .336.
He's batted .417 with two home runs and nine RBIs during a 12-game hitting streak against the Brewers this season.
Wong went 0 for 8 in his first three games since making his much-anticipated major league debut Friday, but is 5 for 10 in the last two.
Teammate Matt Holliday has followed a 12-game hitting streak by going 1 for 19 through the first five of this six-game trip. However, he's 5 for 10 with a homer against Milwaukee starter Tom Gorzelanny (3-4, 2.95).
After he gave up three hits in seven innings of a 10-0 victory at Seattle on Aug. 10, the left-hander allowed five runs and two homers in 4 2-3 innings Friday in a 7-6 win over Cincinnati.
Gorzelanny has a 3.60 ERA in five relief appearances this season against the Cardinals, but has not faced them as a starter since 2011. He's 2-5 with a 4.85 ERA in nine starts versus St. Louis.
Rookie first baseman Sean Halton had two hits with three RBIs on Tuesday for the Brewers, who snapped a five-game home skid to St. Louis.
Halton was 0 for 10 with five strikeouts in his previous eight games.
Milwaukee All-Star Carlos Gomez could miss a sixth straight game with a knee injury.